For many years, the conventional way to attach a trailer to a vehicle hitch was to utilize a standard "S" hook and chain. However, the "S" hook/chain mechanism, while simple to use, has a number of safety deficiencies. For example, the chain can become detached from the "S" hook quite easily when the vehicle/trailer engages rough terrains, potholes or bumps, and other uneven road surfaces, thereby causing the trailer to become disengaged from the vehicle. In addition, the "S" hook does not enable the user to restrict the amount of slack in the chain, resulting in loose chain between the trailer and the vehicle, which can contribute to the danger of the chain detaching from the "S" hook.
Recently, laws have been enacted mandating certain safety requirements in the manner in which trailers are connected to vehicles. A California statute now requires that "All safety connections and attachments shall have a positive means of ensuring that the safety connection or attachment does not become dislodged while in transit." And further states that "No more slack shall be left in a safety chain than is necessary to permit proper turning". Accordingly, a new safety lock device is required having a positive self-locking mechanism to eliminate the possibility of dislodgement and which enables adjustment to remove unnecessary slack from the safety chain.